CMT 1A: Age-related changes in motor unit number estimates in adult patients

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Eur J Neurol. 2010 Apr 27

Age-related changes in motor unit number estimates in adult patients with

Charcot-Marie-Tooth type 1A.

van Dijk JP, Verhamme C, van Schaik IN, Schelhaas HJ, Mans E, Bour LJ, Stegeman

DF, Zwarts MJ.

Department of Neurology/Clinical Neurophysiology, Radboud University Nijmegen

Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Nijmegen.

Abstract

Background: Charcot-Marie-Tooth disease type 1A (CMT1A) is known as a

demyelinating hereditary neuropathy. Secondary axonal dysfunction is the most

important determinant of disease severity.

In adult patients, clinical progression may be because of further axonal

deterioration as was shown with compound muscle action potential (CMAP)

amplitude reductions over time. The motor unit number estimation (MUNE)

technique may be more accurate to determine the number of axons as it is not

disturbed by the effect of reinnervation.

The purpose of this study was to investigate the number and size of motor units

in relation to age in patients and controls.

Methods: In a cross-sectional design, we assessed arm and hand strength and

performed electrophysiological examinations, including CMAP amplitudes and MUNE

of the thenar muscles using high-density surface EMG in 69 adult patients with

CMT1A and 55 age-matched healthy controls.

Results: In patients, lower CMAP amplitudes and MUNE values were related to hand

weakness. The CMAP amplitude and MUNE value of the thenar muscles were

significantly lower in patients than in controls. CMAP amplitudes declined with

age in controls, but not in patients. MUNE values declined with age in both

patients and controls.

Conclusions: The age-dependent decrease in the number of motor units was not

significantly different between patients with CMT1A and controls, indicating

that loss of motor units in adult patients is limited.